The invention relates to the field of power conversion and in particular to the field of alternating current power conversion.
It is well known to provide power converters for converting electrical power from one form into a different form that is useable under many specific circumstances for powering electrical load devices. For example, it is known to provide a direct current (DC) power supply that converts alternating current (AC) power into DC power for supplying DC electrical power to mobile devices.
Additionally, it is known to provide an AC/DC power conversion device which is adapted to perform the power conversion in accordance with the power sources available in different countries. Another well known type of power conversion is the AC/DC type of conversion that is performed by light dimmers, wherein the peak-to-peak voltage of the output is maintained substantially the same as the peak-to-peak voltage of the input while the power conversion is accomplished by changing the duty cycle of the output.
Commercial power in Europe is supplied at 220 VAC with a frequency of 50 Hertz (Hz). In the United States the standard voltage supplied is 120 VAC at 60 Hz. In addition, brownouts may significantly reduce a line voltage below the standard level and, conversely, lighter loads, particularly at night, may cause the line voltage to increase above the standard level. Additionally, corresponding variations in frequency are possible. Accordingly, power converters operating on the standard power suppliers to provide a DC source are typically designed to operate at frequencies between 47 and 65 Hz and with voltages ranging from 85 VAC to 265 VAC.
Typically such a DC power supply converts an AC input voltage to a DC output voltage using an electromagnetic interference filter, a power factor correction circuit and a DC to DC converter. The electromagnetic interference filter is used in order to insure compliance with applicable electromagnetic interference standards. The power factor correction circuit converts AC power to a high DC voltage. For example, the high DC voltage can be 400 VDC. The DC to DC converter scales the high DC voltage down to a lower DC voltage as required by the load equipment to be powered by the power supply.
U.S. Pat. No. 5,949,671, issued to Lee on Sep. 7, 1999 and entitled xe2x80x9cPower Supply With Re-Configurable Outputs For Different Output Voltages and Methods Of Operation Thereofxe2x80x9d teaches a type of DC power supply that is well known in the prior art. The DC power supply taught by Lee has a pair of output rectifying circuits that are coupled in alternate configurations to provide dual voltages at an output of the DC power supply. The voltage supply taught by Lee is thus capable of providing different output voltages using a single voltage controller.
U.S. Pat. No. 4,626,981, issued to Su on Dec. 2, 1986 teaches a dual voltage converter circuit. The dual voltage converter circuit taught by Su converts an AC input voltage into an AC output voltage having a predetermined amplitude. The output voltage is coupled to a load circuit in order to energize the load circuit. When a relatively low amplitude AC mains supply voltage is applied to the converter the entire AC mains supply voltage is selectively coupled to a degaussing circuit without substantial amplitude change. On the other hand, when a relatively high amplitude AC mains supply voltage is provided a portion of the amplitude of the input AC mains supply voltage having an amplitude that approximates that of a lower AC mains supply voltages is coupled to the degaussing circuit.
Su also teaches coupling an AC input voltage to a rectifier arrangement of a voltage converter to develop DC voltages in a pair of capacitors. The rectifier arrangement combines the AC input voltage with the voltages in the first and second capacitors, respectively, to produce an output voltage. The output voltage energizes an AC utilization circuit such as a degaussing circuit.
During the positive portion of each cycle of the AC input voltage, the rectifier arrangement couples a positive difference voltage to the degaussing circuit. The positive difference voltage is formed between the positive portion of the AC input voltage and the voltage in the first capacitor to produce a positive level of the degaussing voltage. During the negative portion of each cycle of the AC input voltage, the rectifier couples a negative difference voltage to the degaussing circuit. The negative difference voltage is formed between the negative portion of the AC input voltage and the voltage in the second capacitor to produce a negative level of the degaussing voltage.
However, the power converters taught by Lee and Su are suitable only for resistive loads. They are not suitable for powering devices having electronic loads primarily because of voltage spikes and other signal distortions present in the output voltage signals of these converters. For example, a 120 volt rms signal at the output of a converter such as the one taught by Su may have peaks approaching those of a 240 volt signal. Such peaks can destroy electronic circuitry.
U.S. Pat. No. 4,314,327, issued to DePuy on Feb. 2, 1982, entitled xe2x80x9cTransistor Drive Control For A Multiple Input DC To DC Converterxe2x80x9d is an example of another type of prior art electrical energy conversion circuit. The conversion circuit taught by DePuy operates with major and minor variations in the level of applied input DC voltage and reduces the computational losses of its switching transistors that may other occur for the major and minor increases of the input DC voltage.
A base drive current circuit in the DuPuy converter includes a full wave rectifier and multiple level current limiting circuit which is interposed between a base drive winding of a saturable transformer and the base electrodes of the transistors of first and second transistor diode combinations. The base drive current circuit adapts the saturation condition of the first and second transistor diode combinations to the level of the applied DC input voltages. This reduces the level of increase of the computational losses of the transistor diode combinations.
Kruppa, in U.S. Pat. No. 5,805,439 issued on Sep. 8, 1998, teaches a DC to DC automatic switching circuit. The Kruppa device is a circuit for controlling multiple DC input voltages to produce a predetermined output voltage using a single DC to DC converter. Sensing of the DC input voltages supplied to the Kruppa switching device permits automatic switching in order to route an applied voltage between input terminals and output terminals. Furthermore, this switching permits configuring of a feedback network that selects the output voltage of the DC to DC converter.
U.S. Pat. No. 5,654,884, entitled xe2x80x9cMultistand AC/DC Converter With Baseline Crossing Detectionxe2x80x9d issued to Mohan on Aug. 5, 1997 provides circuitry for use in an integrated circuit controlled voltage doubler/bridge circuit. This circuitry is adapted to detect a period during which there is a lack of AC supply voltage following a period of AC input voltage within a predetermined range of values. When this occurs repeated triac firing pulses are provided such that the AC supply is rectified and doubled as soon as the AC supply voltage returns.
Thus, it is known in the prior art to provide AC to AC converters which are not suitable for use with electronic devices. It is also known to provide converters which supply DC electrical energy suitable for use with electronic devices from an AC or a DC input. However, none of these devices are capable of providing AC/DC energy conversion suitable for use with electronic devices. It is known to solve these problems using a transformer. However, the use of a transformer increases the size, weight and cost of a power conversion device.
A method for performing power conversion in a power converter device provides a converter output AC waveform from a converter input AC waveform, the convertor input waveform having an input power level, an input frequency, an input waveform shape, and an input voltage/current characteristic. The converter input AC waveform is applied to a converter switch having a converter switch frequency and the switch is operated at the converter switch frequency to provide a switched waveform, the switched waveform having a plurality of switched waveform notches with a notch repetition rate substantially equal to the converter switch frequency. A filter performs filtering of the switched waveform to provide the converter output AC waveform having an output power level substantially equal to the input power level, an output frequency substantially equal to the input frequency, an output waveform shape substantially similar to the input wave form shape, and an output voltage/current characteristic substantially different from the input voltage/current characteristic.
The output voltage/current characteristic has an output voltage level substantially less than an input voltage level of the input voltage/current characteristic and an output current level substantially higher than an input current level of the input voltage/current characteristic. The converter input AC waveform has a positive half cycle and a negative half cycle and the switched waveform notches are formed during both the positive half cycle and the negative half cycle of the converter input AC waveform. The input waveform shape can be a sine wave and the output waveform shape can be a sine wave. Additionally, the input waveform shape can be a square wave and the output waveform shape can be a square wave.
The converter switch frequency is substantially higher than the input frequency and the filtering is performed by a filter having a filter a corner frequency that is at least twice as high as the input frequency. The converter switch frequency is substantially higher than the filter corner frequency. The filter has a frequency spectrum including a snitching component of the converter switch wherein the attenuation of the switching component by the filter is determined in accordance with the relationship: Attenuation in dB=12*log2(Fsw2Fin) and Fsw represents the converter switch frequency and 2Fin represents the filter corner frequency.